Liquid Distributors and Redistributors

Liquid distributors for scrubber applications fall into two main categories, Gravity type and Spray type distributors. Gravity type distributors rely on gravity to provide the necessary energy to disperse the liquid through the distributor and eventually across the packing surface. Gravity distributors are available in either Orifice or Weir type. One benefit of the Gravity type distributor is the low turn-down ratio. These types of distributors function equally well at both low and high liquid flow rates and do not require high influent liquid pressure. All of the gravity type distributors are fabricated in sections to allow for ease of installation through the vessel manways. Each can be made from a variety of plastics, fiberglass, or exotic metals. Gravity type distributors should not be used if the recirculation liquid can solidify at ambient conditions.

The Orifice type distributor utilizes a full cross-sectional plate with numerous holes drilled through the bottom to allow the liquid to drain down on to the packing surface. The plate has raised edges, to prevent the liquid from running down the wall of the vessel. The plate is also equipped with vertical pipes to allow the treated air to pass through for discharge. The orifice type distributor is best suited for small tower applications due to the limitations of free area for the process air to pass through.

The other gravity type liquid distributor is the Weir type. Weir type distributors are available in two basic configurations: Pipe and Trough styles. The Pipe style is constructed of a main pipe, which drains to numerous lateral pipes, which distribute the liquid across the packing. The Trough type works basically the same as the pipe type except it utilizes troughs instead of pipe. The trough type allows for greater flow volumes and can be used with larger vessels. Both the Trough and Pipe type have large free area for air passage.

Spray header assemblies are used when the liquid is being fed under pressure and the nozzles are used to distribute a specific pattern across the surface area. There are a variety of nozzles available, all with different design criteria. Nozzles can be fabricated from thermoplastics and metals. We have been designing these assemblies for many years, and as such have a tried and true method for determining the proper nozzles for your application.

Redistributors can be used as well if chemical consumption is a concern a redistributor collects the down coming liquid from the bed above and distributes it evenly over the packing.

There are four basic advantages to using a redistributor:
1. higher liquid handling capacity,
2. elimination of wall streaming,
3. non-fouling design,
4. constant percentage of free space, regardless of tower diameter.

Redistributors can be equipped with wall wipers to collect the liquid clinging to the tower walls.

Packing Support Plates

The basic purposes of a Packing Support Plate are twofold: one, to physically support the weight of the packed bed, and two, to allow separate passages for the liquid and gas streams, so as not to have the streams struggle for the same passageway. Packing support plates are available in many different configurations and designs. Most often, for gas injection plates, a beam type design is utilized to maximize surface area. Gas injection plates can be constructed of ceramic, FRP, plastics, and a variety of exotic alloys. For randomly dumped packing, a grating type support plate is an option. A grate support is basically just that, a grate laid out to support the weight of the packing; usually constructed of fiberglass, stainless steel, or an exotic alloy.

Hold Down Plates and Bed Limiters

Holds down plates are used when there is a high pressure drop or if surges are foreseen, to prevent the packed bed from becoming fluidized and breaking up. Ideally, hold down plates should be designed to restrict the smallest piece of packing from exiting the packed bed, however, this is not always possible as most tower design requires a minimum of 70% free area to be available. Hold down plates can be constructed from thermoplastics, FRP or metal. Bed limiters, in function, are very similar to hold down plates. Bed limiters are meant to prevent the passage of packing. They are usually fastened to the tower wall or suspended from the liquid distributor/support ledge above. Bed limiters can also be constructed from thermoplastics, FRP or a variety of metals.

Packing Media

Packing media can be constructed from a variety of plastics (polypropylene, polyethylene, etc.), or metal, depending on the application in which it will be used. Also, packing is available in a variety of different sizes. The air stream contaminants and the liquid being fed through the distributor will determine the size, construction, configuration, and material of the packing.